Assessment and Design of Seismically Isolated Bridges in Proximity of Major Faults and Located on Liquefiable Soils

Abstract eng:
In this paper, seismic isolation design of one highway viaduct and one high-speed railway viaduct located within few hundred meters of North Anatolian fault in Turkey is studied. Strong near-field characteristics such as directivity and liquefaction are expected due to soft soil conditions under the scenario earthquake. Seismic assessments of viaducts are performed considering these unfavorable effects. For the highway viaduct, a hybrid seismic isolation system is chosen for the bridge consisting of four natural and two lead-rubber bearings supporting the six steel-girders at each substructure. Lead cores in the lead-rubber bearings are designed to have an overall characteristic strength equal to 10% of the superstructure weight. This large characteristic strength is intentionally chosen to limit the isolator displacements under near-field effects. Furthermore, the supplementary four natural rubber bearings over each substructure provided additional stiffness to achieve a small post elastic period. For the railway viaduct, the same design philosophy was followed with considering the serviceability issues related to high-speed railway bridges. Since yield displacement of leadrubber bearings are about 2-3 cm, which is unsatisfactory for stringent displacement limits specified in international railway codes, in this case curved surface slider bearings having a dynamic friction coefficient of 12% with 2.54 mm yield displacement are selected.

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